Alcohol as a modifiable lifestyle factor affecting multiple sclerosis risk.

IMPORTANCE: Alcohol consumption may be a modifiable lifestyle factor that affects the risk of developing multiple sclerosis (MS). Results of previous studies have been inconsistent.

OBJECTIVE: To investigate the possible association of alcohol consumption with the risk of developing MS and to relate the influence of alcohol to the effect of smoking.

DESIGN, SETTING, AND PARTICIPANTS: This report is based on 2 case-control studies: Epidemiological Investigation of Multiple Sclerosis (EIMS) included 745 cases and 1761 controls recruited from April 2005 to June 2011, and Genes and Environment in Multiple Sclerosis (GEMS) recruited 5874 cases and 5246 controls between November 2009 and November 2011. All cases fulfilled the McDonald criteria. Both EIMS and GEMS are population-based studies of the Swedish population aged 16 to 70 years. In EIMS, incident cases of MS were recruited via 40 study centers, including all university hospitals in Sweden. In GEMS, prevalent cases were identified from the Swedish national MS registry. In both studies, controls were randomly selected from the national population register, matched by age, sex, and residential area at the time of disease onset.

MAIN OUTCOME AND MEASURE: Multiple sclerosis status.

RESULTS: There was a dose-dependent inverse association between alcohol consumption and risk of developing MS that was statistically significant in both sexes. In EIMS, women who reported high alcohol consumption had an odds ratio (OR) of 0.6 (95% CI, 0.4-1.0) of developing MS compared with nondrinking women, whereas men with high alcohol consumption had an OR of 0.5 (95% CI, 0.2-1.0) compared with nondrinking men. The OR for the comparison in GEMS was 0.7 (95% CI, 0.6-0.9) for women and 0.7 (95% CI, 0.2-0.9) for men. In both studies, the detrimental effect of smoking was more pronounced among nondrinkers. CONCLUSIONS AND RELEVANCE; Alcohol consumption exhibits a dose-dependent inverse association with MS. Furthermore, alcohol consumption is associated with attenuation of the effect of smoking. Our findings may have relevance for clinical practice because they give no support for advising patients with MS to completely refrain from alcohol.